In the development of electronic musical instruments, such as electronic organs, chord selection systems have been developed which permit the musician to form chords from the keyboard or accompaniment manual by depressing a single key representative of the root note of the desired chord. Additional circuitry in the organ has been provided to provide alternate application of the chord parts to the output transducers of the organ or to provide a rhythmic application of the chord in accordance with preset controls on the organ. While chord playing systems of this type have met with wide commerical acceptance, the pre-programmed chord parts limit the number of musical keys which can be played by the musician to those imposed in the original design of the organ. More accomplished musicians who might wish to take advantage of the extended capabilities which are made possible by such one-note chord producing systems may find it difficult to work within the limitations imposed, which generally permit the playing of only major chord triads when the instrument is placed in its automatic chord or one-note chord mode of operation.
Some prior art organs increased the flexibility available to a musician in such one-note chord systems, by causing the depression of the root note key to simultaneously initiate operation of or couple tone generators for the fifth parts and the major and minor third parts of a chord. An additional switch then is provided to select either the minor third or the major third part for ultimate reproduction along with the root and fifth parts in an output transducer. In some cases, this switch is a separate manual switch which may be foot operated, knee operated, or operated in the manner of the control tabs of the organ. In one position of the switch, major chords are produced; in a different position of the switch, minor chords are produced. While this does increase the flexibility of the instrument, it is necessary for the musician to operate this additional switch whenever he wants to make a change from a minor chord to a major chord or vice-versa. To a beginning musician, the imposition of this additional requirement of operating such a switch tends to complicate the playing of the instrument.
In order to expand the flexibility of one-note chord producing systems, a prior art system has been developed in which the musician can preselect the key which is to be played. Once this has been done, depression of any of the root note playing keys which generate the chords, then causes either a major chord or a minor chord to be produced in accordance with a pre-established relationship of the note produced by the playing key to the musical key selected in advance. Some of the root notes played in an octave then will produce major chords, and others will produce minor chords in accordance with the pre-established musical key.
While this type of system does provide increased flexibility to the musician, there still is imposed upon the musician an unnecessary constraint which makes it difficult for him to make major chord to minor chord transpositions at will. In fact, the musician in such a system has no control over the particular chord produced by depression of a playing key. If he wishes to make a major chord to minor chord transposition with respect to any particular playing key, it also is necessary for him to know which musical key he must select to effect this transposition. Then he must operate a separate switch to select the musical key which will give him the result he desires.
It is desirable to provide in an electronic organ a chord playing system which permits the musician to play a single note, the root note, for the chord, with the rest of the chord being automatically produced; but which gives the musician control over whether the chord produced is a major or minor chord without requiring him to operate additional switches with his feet, knees, or hands.